This invention relates to electrical interconnection systems, and more particularly, to a power changeover apparatus which is readily incoporated in aircraft, space vehicles and the like.
Computer controlled apparatus such as guidance systems, navigation instruments and the like require the application of backup power instantaneously, when primary power is lost, interrupted or turned off, to allow time for orderly shut-down of the apparatus. After such orderly shut-down, it is desirable that the apparatus present no load to the backup power source.
An orderly shut-down is desirable in many applications so that the logic circuits of the computer can be restored to a known state when the computer apparatus is once again powered up. This requirement is particularly desirable in avionics equipment on board aircraft or spacecraft. Additionally, multiple redundancy in computer controlled apparatus and the use of multiple redundant power supplies increases the necessity for an orderly shut-down in these applications.
Prior art power changeover systems have utilized electromechanical devices such as relays to provide isolation and changeover; however, because of mechanical limitations, such devices are incapable of providing the required instantaneous substitution of the backup power source for the failing primary power source. See, for example, U.S. Pat. Nos. 3,419,779 and 4,044,268, which are useful background and are hereby incorporated by reference. Fast electronic switches have been used in the prior art as power changeover devices, however, such devices do not provide isolation of the load from the backup power source after shut-down. See U.S. Pat. No. 3,454,781, also incorporated herein by reference thereto.